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In theory if the lenses were perfectly manufactured with no optical faults and were exactly the same and you had the same aperature, the image would look the same.

However, in practice quality and lens construction varies, even 2 lenses exactly the same model would vary(although this would be minimal).

The other thing to keep in mind is that lenses don't perform their best at extremes e.g. for the 18-55mm lens, it might suffer from more barrel distorition or have more chromatic aberrations at 18mm. Generally you will lose some sharpness at the extremes.

In theory if the lenses were perfectly manufactured with no optical faults and were exactly the same and you had the same aperature, the image would look the same.

However, in practice quality and lens construction varies, even 2 lenses exactly the same model would vary(although this would be minimal).

The other thing to keep in mind is that lenses don't perform their best at extremes e.g. for the 18-55mm lens, it might suffer from more barrel distorition or have more chromatic aberrations at 18mm. Generally you will lose some sharpness at the extremes.

I'm guessing Manda does'nt even know about barrel distortion , Let alone Chromatic aberations , This is a new to photography thread and I kept my answer to the question as simple as I could , But you are right , Still 55mm is 55mm

I think Manda might be onto something that has not been fully addressed yet.
Correct me if I'm wrong, but isn't DOF is affected by the aperture of a lens? In other words, the lower the numeric f-stop, the shallower the DOF.
Assuming Manda is talking about EF-S lenses, using 18-55 at 55mm the maximum aperture is 5.6. If swapping to a 55-250mm, then at 55mm this lens has a maximum aperture of 4.5.